This environmental-quality invention is in the field of chemical conversion coatings formed on aluminum and aluminum alloy substrates. One aspect of the invention is an improved process of forming an oxide coating, referred to as a xe2x80x9ccobalt conversion coating,xe2x80x9d that is chemically formed by oxidizing the surface of an aluminum or aluminum alloy substrate. The invention enhances the quality of the environment of mankind by contributing to the maintenance of air and water quality. The term xe2x80x9caluminumxe2x80x9d as used herein includes aluminum and aluminum alloys.
Reference is made to the following patents, which are incorporated by reference herein: U.S. Pat. No. 5,298,092, issued Mar. 29, 1994; U.S. Pat. No. 5,415,687, issued May 16, 1995; U.S. Pat. No. 5,472,524, issued Dec. 5, 1995; U.S. Pat. No. 5,487,949, issued Jan. 30, 1996; U.S. Pat. No. 5,378,293, issued Jan. 3, 1995; U.S. Pat. No. 5,411,606, issued May 2, 1995; U.S. Pat. No. 5,551,994, issued Sep. 3, 1996; and U.S. Pat. No. 5,873,953, issued Feb. 23, 1999.
Recently, I have made significant improvements to this technology to further improve bath life and bath stability as well as coating performance characteristics. The details are described below.
Environmental regulations in the United States are mandating drastic reductions of allowed chromium compounds in effluent as well as emissions into the air which are generated from metal finishing processes. I have devoted considerable effort to the development of a non-chromated surface coating as a replacement for current chromated processes as detailed in MIL-C-5514 and Boeing Process Specification BAC 5719.
Chromium containing conversion coatings are used by The Boeing Company, its subcontractor base and generally throughout the industry. Solutions used to produce these conversion coatings contain carcinogenic hexavalent chromium, fluorides, and cyanides, all of which present a significant environmental, health, and safety problem. The constituents of a typical chromate conversion-coating bath are as follows: CrO3 xe2x80x9cchromic acidxe2x80x9d (hexavalent); NaF sodium fluoride; KF4B potassium tetrafluoborate; K2ZrF6 potassium hexafluorozirconate; K3Fe(CN)6 potassium ferricyanide; and HNO3 nitric acid.
Current chromium conversion films are deposited by immersion, meet a 168-hour corrosion resistance requirement when tested to ASTM B117, but also serve as a surface substrate to promote paint adhesion. Typical coating weights of these chromium films range from 40 to 120 mg/ft2 and do not cause a fatigue life reduction of the aluminum substrate.
In one aspect the invention is an improved process that is commercially practical for forming an oxide film cobalt conversion coating exhibiting corrosion resistance and paint adhesion properties on a substrate, where the substrate is aluminum or aluminum alloy, the process including the steps of:
(a) providing an oxide film forming cobalt conversion solution comprising an aqueous reaction solution, containing no triethanolamine (TEA), prepared by reacting the following starting materials:
(1) a water soluble cobalt-II salt CoX2 where X=Cl, Br, NO3, CN, SCN, ⅓PO4, xc2xdSO4, xc2xdCO3, formate, or acetate;
(2) a water soluble complexing agent selected from the group consisting of MeNO2, MeAc, MeFm, NH4Ac, and NH4Fm where Me is Na, K, or Li; Ac is acetate; and Fm is formate;
(3) an accelerator selected from the group consisting of NaClO3, NaBrO3, and NaIO3;
(4) water; and
(b) contacting the substrate with the aqueous reaction solution for a sufficient amount of time to oxidize the surface of the substrate, whereby the oxide film cobalt conversion coating is formed, thereby imparting corrosion resistance and paint adhesion properties to the substrate.
In another aspect the invention is a chemical conversion coating solution that is commercially practical for producing an oxide film cobalt conversion coating on an aluminum or aluminum alloy substrate, said solution comprising an aqueous reaction solution, containing no triethanolamine (TEA), prepared by reacting the following starting materials:
(1) a water soluble cobalt-II salt CoX2 where X=Cl, Br, NO3, CN, SCN, ⅓PO4, xc2xdSO4, xc2xdCO3, formate, or acetate;
(2) a water soluble complexing agent selected from the group consisting of MeNO2, MeAc, MeFm, NH4Ac, and NH4Fm, where Me is Na, K, or Li; Ac is acetate; and Fm is formate;
(3) an accelerator selected from the group consisting of NaClO3, NaBrO3, and NaIO3;
(4) water.
In yet another aspect the invention is an improved process that is commercially practical for forming an oxide film cobalt conversion coating exhibiting corrosion resistance and paint adhesion properties on a substrate, where the substrate is aluminum or aluminum alloy, the process comprising the steps of:
(a) providing an oxide film forming cobalt conversion solution comprising an aqueous reaction solution, containing no triethanolamine (TEA), prepared by reacting the following starting materials:
(1) a water soluble cobalt-II salt CoX2 where X=Cl, Br, NO3, CN, SCN, ⅓PO4, xc2xdSO4, xc2xdCO3, formate, or acetate;
(2) an ammonium salt NH4X where X=Cl, Br, NO3, CN, SCN, ⅓PO4, xc2xdSO4, ⅓CO3, formate, or acetate;
(3) ammonium hydroxide (ammonia);
(4) an accelerator selected from the group consisting of NaClO3, NaBrO3, and NaIO3;
(5) water; and
(b) contacting the substrate with the aqueous reaction solution for a sufficient amount of time to oxidize the surface of the substrate, whereby the oxide film cobalt conversion coating is formed, thereby imparting corrosion resistance and paint adhesion properties to the substrate.
And in yet another aspect the invention is a chemical conversion coating solution that is commercially practical for producing an oxide film cobalt conversion coating on an aluminum or aluminum alloy substrate, the solution comprising an aqueous reaction solution, containing no triethanolamine (TEA), prepared by reacting the following starting materials:
(1) a water soluble cobalt-II salt CoX2 where X=Cl, Br, NO3, CN, SCN, ⅓PO4, xc2xdSO4, xc2xdCO3, formate, or acetate;
(2) an ammonium salt NH4X where X=Cl, Br, NO3, CN, SCN, ⅓PO4, xc2xdSO4, xc2xdCO3, formate, or acetate;
(3) ammonium hydroxide (ammonia);
(4) an accelerator selected from the group consisting of NaClO3, NaBrO3, and NaIO3; and
(5) water.